This relates generally to imaging devices, and more particularly, to imaging devices having image sensor pixels with different sensitivities.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels arranged in pixel rows and pixel columns. The image pixels include photodiodes that generate charge in response to image light during an exposure time. The image pixels convert the generated charge into analog image signals that are read out by pixel readout circuitry. The photodiodes have a charge storage capacity indicative of the amount of charge that can be stored on the photodiodes. Image pixels are often provided with color filter elements for generating image signals in response to different colors of light. Pixels with certain color filter elements may be more sensitive to light than pixels with other color filter elements (i.e., more sensitive pixels may generate charge on the corresponding photodiode faster than less sensitive pixels).
Conventional image sensors typically require use of the same integration time for all colors in order to avoid motion artifacts in the final captured image. Due to different sensitivities of image pixels of different colors, under a given color temperature illumination, the full charge storage capacity may not be utilized for several of the less sensitive color channels in the image sensor (i.e., because the charge capacity of the more sensitive image pixels is filled before the charge capacity of the less sensitive image pixels). For example, in image sensors having red, green, and blue pixels, red and blue pixels may not utilize the full charge capacity of the corresponding photodiodes as more photons are available in the green spectral range of the green image pixels. As the maximum signal-to-noise ratio of the generated image signals generally increases as the square root of the number of captured photons, less sensitive image pixels often have a reduced maximum signal-to-noise ratio when the array is formed with more sensitive image pixels than when all of the pixels have similar sensitivities.
It would therefore be desirable to be able to provide imaging devices with improved means for capturing and processing images.